Increasing the size or growth rate of a commercially valuable plant provides a number of important practical applications, and may contribute to an increase in yield. For example, increasing the size of a cultivar may generate higher yield of the edible vegetative portion a crop plant. Increasing the size and/or growth rate of a plant may also provide a competitive advantage in the field. Many weeds outgrow slow-growing young crops or out-compete them for nutrients, and thus it is usually desirable to use plants that establish themselves quickly. Seedlings and young plants are also particularly susceptible to stress conditions such as salinity or disease. Increasing seedling growth rate and shortening the time to emergence from soil contributes to seedling vigor, aids seedlings in coping with these stresses, and may allow these crops to be planted earlier in the season. Early planting helps add days to a critical seed or grain-filling period and increases yield. Modification of the biomass of other tissues, such as root tissue, may be useful to improve a plant's ability to grow under harsh environmental conditions, including drought, high salt or nutrient deprivation, because larger roots may better reach or take up water or nutrients.
For many plants, including fruit-bearing trees, plants that are used for biofuels, trees that are used for lumber production, or trees and shrubs that serve as view or wind screens, increased stature provides improved benefits in the forms of greater yield or improved screening.
Increased leaf size may also be of particular interest. Increasing leaf biomass can be used to increase production of plant-derived pharmaceutical or industrial products. An increase in total plant photosynthesis is typically achieved by increasing leaf area of the plant. Additional photosynthetic capacity may be used to increase yield derived from particular plant tissue, including leaves, roots, fruits or seed, or permit better growth of a plant under both decreased and high light intensity.
However, increasing the size or growth rate of a plant may require controlling a number of regulatory and synthetic pathways. Transcription factors are proteins that influence the expression of a particular gene or sets of genes. Altering the expression of one or more transcription factors may provide the necessary control to manipulate complex biochemical or morphological traits in a plant, and thus multiple cellular processes. This application demonstrates that transformed plants that comprise cells having altered levels of at least one of the closely-related transcription factors of the invention exhibit increased size and/or growth rate relative to control plants.